Volume of Pipe= 0.785 x (dia.)² x length of pipe=cu.ft.
Volume of Pipe = 0.785(.5)²x 1’ = 0.19625 cu.ft
Formula: (0.785 constant)
Use the formula below to change inches to fraction of a foot.
6” pipe.
6” ÷ 12”=.5 ft > Therefore, 6 inch pipe is equal to .5 ft. So in the formula above instead of using 6 inches in the (dia.), use .5. The length of pipe could now be multiplied in feet.
To further complicate matters; if you need precision, you have to consider the tolerance of the pipe as well.
Most piping fabrication standards allow wall thickness to deviate up to 12.5% under the nominal size. So if you are calculating volume based on nominal size, your actual volume may be slightly higher due to less wall thickness.
Charles